The present invention relates to a voltage regulator circuit with functions of output short-circuit protection and output overcurrent protection and an integrated circuit device including the voltage regulator circuit.
FIG. 1 is a circuit diagram showing the structure of a conventional voltage regulator circuit, which is disclosed in Japanese Patent Kokai (Laid-open) Publication No. 2001-306163, for example. As shown in FIG. 1, the voltage regulator circuit includes an input terminal REGin for a reference voltage Vref1, an operational amplifier OP1, a regulator output terminal REGout, resistors R1, R2, and R3, and PNP transistors Q1 and Q2. The operational amplifier OP1 outputs a control voltage V2 depending on a difference between a feedback voltage V1 at a node nd1 between the resistors R1 and R2 and the reference voltage Vref1, to a node nd2 which is connected to the base of the PNP transistor Q1. The PNP transistor Q1 allows a current I1 depending on the control voltage V2 to flow, thereby stabilizing an output voltage Vout from the regulator output terminal REGout. If an abnormality in an external load circuit (not shown in FIG. 1) connected to the regulator output terminal REGout causes an overcurrent to flow from the regulator output terminal REGout, a voltage V3 at a node nd3 between the resistor R3 and the PNP transistor Q1 drops; the PNP transistor Q2 is turned on; the control voltage V2 of the node nd2 increases to a high level close to the power supply voltage VDD; the PNP transistor Q1 is turned off; and the regulator output voltage Vout from the regulator output terminal REGout decreases to a low level close to the ground voltage VG at the ground GND.
The above-mentioned conventional voltage regulator circuit, however, stops monitoring the status of the external load circuit connected to the regulator output terminal REGout after it detects an output overcurrent and turns off the PNP transistor Q1, that is, after it enters the overcurrent protection state. Accordingly, even if the external load circuit recovers to the normal state, the voltage regulator circuit does not automatically return from the overcurrent protection state to the normal operation state, thereby maintaining the overcurrent protection state until a reset operation is made.